As soon as I knew Natsume was continuing, that was a must on my list.
I've pleasantly fallen in love with Usagi Drop.
Kamisama Dolls, Blue Exorcist, and No. 6 are all on my watch list, but they don't compare to the excitement I get when I know another Usagi Drop is out.
Hanasaku Iroha, Bleach, and Naruto are continuations that I've already set myself in to, so I wouldn't say they're "new" for the summer lineup specifically.